[IMP-dev] providing more control over builds

There is currently no way (as far as I can tell) to tell IMP to build a debug (non-optimized) version. I propose replacing the "release" configure option with a "build" option which can be one of - "debug" which makes a non-optimized version of the library with debugging symbols - "release" which makes an optimized version of the library but with runtime checks enabled - "fast" (or some better name, perhaps "ndebug") which used NDEBUG to disable runtime checks (and is optimized and doesn't have debugging symbols).